Look at a candle, or any other luminous body, through a plate of glass,
covered with vapour, or dust in a finely divided state, and it will be
surrounded with a ring of colours, like a halo round the sun or moon.
These rings increase with the size of the particles which produce them;
and their brilliancy and number depend on the uniform size of these
particles.
Or, haloes may be imitated by crystallizing various salts upon thin
plates of glass, and looking through the plate at a candle or the sun.
For example, spread a few drops of a strong solution of alum over a
plate of glass so as to crystallize quickly, and cover it with a crust
scarcely visible to the eye. Then place the eye close behind the
smooth side of the glass plate, look through it at a candle, and you
will perceive three fine haloes at different distances, encircling the
flame.